1. Field of the Invention
This invention relates to a manufacturing method of lighting device, specifically to a manufacturing method of lighting device using a light-emitting device with improved thermal dissipation.
2. Description of the Related Art
Electric lamps are commonly used when large amount of lighting is required. In some cases where a lighter, thinner and smaller lighting device is required, printed circuit boards with light-emitting elements, such as the one shown in FIG. 10, are used.
Although the light-emitting elements are light-emitting diodes (hereinafter referred to as LED) in most cases, semiconductor lasers or the likes are also conceivable.
The light-emitting element 2 is provided with two leads 3 and 4. The backside (anode or cathode) of the LED 5 is soldered to one of the leads 3, and the other lead 4 is electrically connected to a topside electrode (cathode or anode) of the LED 5 through a metal wire 6. The leads 3 and 4, the LED 5 and the metal wire 6 are encapsulated in transparent sealing resin 7, which also works as a lens.
The leads 3 and 4 are inserted into through holes in the printed circuit board 1 and soldered to electrodes 8 and 9 provided on the printed circuit board 1 for supplying power to the light-emitting element 2.
An example of the light-emitting device using the light-emitting element is described in Japanese Laid Open Patent Publication No. Hei 9-252651.
A drawback is that the size of the printed circuit board 1 is large because the light-emitting element 2 consists of a package which includes sealing resin 7, leads 3 and 4 and so on.
Manufacturers have been competing in development of various structures to realize a smaller, thinner and lighter device. Recently, a wafer scale CSP (chip size package), which has the size comparable to or slightly larger than a die has been developed.
FIG. 11 shows a CSP 12, which adopts a glass epoxy substrate 11 as a supporting substrate, and is slightly larger than a die. Following explanation assumes that an LED 13 is mounted on the glass epoxy substrate 11.
A first electrode (die pad) 14 and a second electrode 15 are formed on a topside of the glass epoxy substrate 11, and a first backside electrode 16 and a second backside electrode 17 are formed on a backside of the substrate. The first electrode 14 is electrically connected to the first backside electrode 16 through a through hole TH, and the second electrode 15 is electrically connected to the second backside electrode 17 similarly.
A bare die of the LED 13 is attached to topside of the die pad 14. A topside electrode of the LED 13 is connected to the second electrode 15 through a metal wire 18. A layer of resin 19 covers an entire surface of the glass epoxy substrate 11 including the LED 13.
The CSP 12 adopts the glass epoxy substrate 11. Unlike the wafer scale CSP, it easily realizes a structure extended from the LED 13 to the backside electrode 16, which is for external connection, and has an advantage of less manufacturing cost.
In a manufacturing method of the CSP 12, firstly copper foils (hereafter referred to as Cu foils) 20 and 21 are attached on both sides of a base material (supporting substrate) of the glass epoxy substrate 11 with an insulative adhesive, as shown in FIG. 11A.
Next, as shown in FIG. 11B, patterning is made to the Cu foils 20 and 21, after areas to form the first electrode (die pad) 14, the second electrode 15 and the first and second backside electrodes 16, 17 are covered with etching-resistant films 22. The patterning could be done on the topside and the backside separately.
Then, as shown in FIG. 11C, holes for the through holes TH are formed in the glass epoxy substrate using a drill or a laser, and the holes are plated to form the through holes TH. The die pad 14 and the first backside electrode 16 as well as the second electrode 15 and the second backside electrode 17 are electrically connected respectively by the through holes TH.
Furthermore, as shown in FIG. 11D, a backside (anode or cathode) of the LED 13 is die-bonded to the die pad 14, which forms a bonding post, after the die pad 14 is coated with nickel and gold plating.
Finally, the topside electrode (cathode or anode) of the LED 13 and the second electrode 15 are electrically connected through the metal wire 18, and covered with the resin layer 19.
Although only one LED 13 is shown on the glass epoxy substrate 11 in FIG. 11, many LEDs are provided in matrix form in practical applications. When necessary, each electric circuit element is separated into individual electric circuit element in final dicing step.
The CSP type electric circuit element, which adopts the glass epoxy substrate as the supporting substrate 11, is completed by the manufacturing method described above. The manufacturing method can be applied also when a flexible sheet is adopted as the supporting substrate.
The LED 13, the first electrode 14, the second electrode 15, the first backside electrode 16, the second backside electrode 17 and the metal wire 18 are components necessary for external connection and protection of the die. It has been difficult to realize a small, thin and light electric circuit element with all of these components.
The glass epoxy substrate, which makes the supporting substrate, is functionally not necessary. However, omitting the glass epoxy substrate 11 is not possible, since it is used in the manufacturing process as the supporting substrate to attach the electrodes.
Therefore the glass epoxy substrate has been adopted and resulted in increased cost. Furthermore, thick glass epoxy substrate has made the circuit element thick, and set a limit for reducing size, thickness and weight.
Another problem is long through hole forming process, which is essential with the glass epoxy substrate 11 or a ceramic substrate in order to connect the electrodes on both sides of the substrate.
Also, there is a problem of increased temperature due to poor heat dissipation of the substrate, which results in increased die temperature and reduced driving capability.
Also, efficiency in use of the light from the LED is not good, because the printed circuit board and the glass epoxy substrate can not direct the light upward, which is emitted from the side of the LED toward the substrate.
The invention provides a manufacturing method of lighting device including providing a conductive foil and forming a plurality of separation grooves in the conductive foil to define portions of the conductive foil to be used as conductive passages. The depth of the separation groove is shorter than a thickness of the conductive foil. An optical semiconductor element is fixed on one of the defined portions of the conductive foil. The optical semiconductor element and the conductive foil are covered with a transparent resin so that the separation grooves are filled with the transparent resin. A backside portion of the conductive foil, which is not covered by the transparent resin, is removed to expose the transparent resin. A portion of the conductive foil having the optical semiconductor element and covered by the transparent resin is separated to provide a light-emitting device. The light-emitting device is mounted on a metal substrate.
A starting material is the conductive foil that is to form the conductive passages. Before being covered by the transparent resin, the conductive foil functions as supporting structure. Once the transparent resin covers the device elements, the resin also functions as supporting structure. Thus, the manufacturing method dispenses with the supporting substrate.
As described above, each light-emitting device covered with the transparent resin is separated by removing the conductive foil of the side on which the separation grooves are not formed and exposing the resin, after the light-emitting devices are covered by the transparent resin to fill the separation grooves. The conductive foil is processed as single sheet until the last processing step, in which each light-emitting device is separated. Thus the workability is improved.